1. Field of the Invention
The present invention relates to a bearing for a fuel pump, which has a multi-layer structure, a method of manufacturing the same, and a fuel pump using the bearing.
2. Related Art
An engine of a vehicle has a low-pressure fuel pump that pressure-feeds a fuel from a fuel tank, to a delivery pipe of a fuel injection valve and a high-pressure pump. The fuel pump, not limited to an in-tank type, sucks fuel to the inside and discharges the fuel to a fuel line or the like. Consequently, the internal components are requested to have corrosion resistance to the fuel (resistance to fuel). Particularly, a bearing for movably supporting the rotary shaft of an armature which rotates at high speed in the fuel pump is demanded very much to have corrosion resistance from the viewpoint of assuring stable rotation of the armature. A conventional bearing is therefore made of a copper-based or brass-based sintered member. Further, a Cu—Zn—Ni—P—C graphite-dispersed Cu-based sintered alloy is disclosed in Japanese Patent Laid-open No. 2001-192754, for example.
Recently, however, a fuel containing a component different from conventional components, such as alcohol fuel is used. Because of global motorization, fuel refined in each country is used for a vehicle and the fuel often contains much oxide, sulfur, and the like. As a result, the corrosion resistance of the conventional bearings is not always sufficient. More particular, it is requested to assure a little clearance between the rotary shaft and the bearing. When corrosion occurs even a little on a sliding layer side on which the rotary shaft slides, it becomes difficult for the rotary shaft to rotate stably. Further, when the corrosion develops, it may cause a lock state of the fuel pump.
There is a method of making the whole bearing of chemically stable carbon (graphite). However, when the whole bearing is made of carbon, a crack or the like easily occurs. Since a method of processing the bearing is limited, the cost increases for assuring dimensional precision.